Figure 2.
Miocene North American drainage. Rio Grande Rift has cut off western headwaters of Mississippi River and created upper Colorado basin, which drains into eastern Great Basin rift. 1—Cypress Hills and Wood Mountain; 2—Upper Missouri River; 3—Eastern Great Basin rift; 4—Early Grand Canyon; HB—Hudson Bay; HS—Hudson Strait; LCL—Lewis and Clark Line; NAMC—Northwest Atlantic Mid-Ocean Channel; RG—Rio Grande; RMT—Rocky Mountain Trench; S SASK—South Saskatchewan River; U. COLO—Upper Colorado River.